U.S. patent application number 10/735615 was filed with the patent office on 2004-12-30 for method for manufacturing gallium nitride-based semiconductor light emitting device.
Invention is credited to Hahm, Hun Joo, Lee, Soo Min, Park, Young Ho.
Application Number | 20040266044 10/735615 |
Document ID | / |
Family ID | 33536217 |
Filed Date | 2004-12-30 |
United States Patent
Application |
20040266044 |
Kind Code |
A1 |
Park, Young Ho ; et
al. |
December 30, 2004 |
Method for manufacturing gallium nitride-based semiconductor light
emitting device
Abstract
Disclosed is a method for manufacturing a gallium nitride-based
semiconductor light emitting device, including the steps of
sequentially forming, over a substrate, a first conductivity type
clad layer, an active layer, and a second conductivity type clad
layer, forming a transparent electrode over the second conductivity
type clad layer, forming a photoresist film on the transparent
electrode such that the transparent electrode is exposed at a
predetermined region corresponding to one lateral end portion
thereof, removing respective portions of the transparent electrode,
second conductivity type clad layer, and active layer corresponding
to the predetermined region, thereby partially exposing the first
conductivity type clad layer, removing the photoresist film, and
forming first and second bonding electrodes on predetermined
portions of the transparent electrode and second conductivity type
clad layer, respectively. In accordance with this method, it is
possible to simplify the whole process, to easily form a
transparent electrode pattern suitable to prevention of
electrostatic discharge (ESD), and to prevent a degradation in the
bonding force of a transparent electrode caused by residual
photoresist.
Inventors: |
Park, Young Ho; (Suwon,
KR) ; Hahm, Hun Joo; (Sungnam, KR) ; Lee, Soo
Min; (Seoul, KR) |
Correspondence
Address: |
LOWE HAUPTMAN GILMAN & BERNER, LLP
Suite 310
1700 Diagonal Road
Alexandria
VA
22314
US
|
Family ID: |
33536217 |
Appl. No.: |
10/735615 |
Filed: |
December 16, 2003 |
Current U.S.
Class: |
438/46 |
Current CPC
Class: |
H01L 33/38 20130101;
H01L 33/42 20130101 |
Class at
Publication: |
438/046 |
International
Class: |
H01L 021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 24, 2003 |
KR |
2003-41173 |
Claims
What is claimed is:
1. A method for manufacturing a gallium nitride-based semiconductor
light emitting device, comprising the steps of: sequentially
forming, over a substrate, a first conductivity type clad layer, an
active layer, and a second conductivity type clad layer; forming a
transparent electrode over the second conductivity type clad layer;
forming a photoresist film on the transparent electrode such that
the transparent electrode is exposed at a predetermined region
corresponding to one lateral end portion thereof; removing
respective portions of the transparent electrode, second
conductivity type clad layer, and active layer corresponding to the
predetermined region, thereby partially exposing the first
conductivity type clad layer; removing the photoresist film; and
forming first and second bonding electrodes on predetermined
portions of the transparent electrode and second conductivity type
clad layer, respectively.
2. The method according to claim 1, wherein the step of partially
exposing the first conductivity type clad layer comprises the steps
of: wet etching the transparent electrode at is portion
corresponding to the predetermined region; and dry etching the
first conductivity type clad layer and active layer at their
portions corresponding to the predetermined region,
respectively.
3. The method according to claim 2, wherein the step of wet etching
the transparent electrode comprises the step of over-etching the
transparent electrode such that the transparent electrode is
undercut beneath the photoresist film by a predetermined width.
4. The method according to claim 3, wherein the predetermined
undercut width of the transparent electrode corresponds to at least
3 .mu.m.
5. The method according to claim 1, wherein the step of forming the
first and second bonding electrodes comprises the steps of: forming
a passivation layer over a light emitting structure obtained after
completion of the formation of the transparent electrode; forming a
photoresist film on the passivation layer such that the passivation
layer is exposed at regions where the first and second bonding
electrodes are to be formed, respectively; etching portions of the
passivation layer respectively corresponding to the electrode
forming regions, thereby removing the passivation layer portions;
forming the first and second bonding electrodes on the electrode
forming regions from which the passivation layer has been removed,
respectively; and removing the photoresist film used to form the
first and second bonding electrodes.
6. A method for manufacturing a gallium nitride-based semiconductor
light emitting device, comprising the steps of: forming a light
emitting structure including a substrate, a first conductivity type
clad layer formed over the substrate, and an active layer, a second
conductivity type clad layer and a transparent electrode
sequentially formed on the first conductivity type clad layer at a
region corresponding to one lateral portion of the first
conductivity type clad layer; forming a passivation layer over the
light emitting structure; forming a photoresist film on the
passivation layer such that the passivation layer is exposed at
predetermined regions where first and second bonding electrodes are
to be formed, respectively; etching portions of the passivation
layer exposed at the predetermined electrode forming regions,
thereby removing the exposed passivation layer portions; forming
the first and second bonding electrodes at the predetermined
electrode forming regions from which the passivation layer has been
removed; and removing the photoresist film.
7. The method according to claim 6, wherein the first and second
bonding electrodes are made of a material selected from a group
consisting of Ti/Al, Cr/Au, Cr/Ni/Au, Cr/Pt/Au, and
Ti/Al/Ni/Au.
8. A method for manufacturing a gallium nitride-based semiconductor
light emitting device, comprising the steps of: sequentially
forming, over a substrate, a first conductivity type clad layer, an
active layer, and a second conductivity type clad layer; forming a
transparent electrode over the second conductivity type clad layer;
forming a photoresist film on the transparent electrode such that
the transparent electrode is exposed at a predetermined region
corresponding to one lateral end portion thereof; etching
respective portions of the transparent electrode, second
conductivity type clad layer, and active layer corresponding to the
predetermined region, thereby partially exposing the first
conductivity type clad layer; forming a passivation layer over a
light emitting structure obtained after completion of the etching
step adapted to partially expose the first conductivity type clad
layer; forming a photoresist film on the passivation layer such
that the passivation layer is exposed at predetermined regions
where first and second bonding electrodes are to be formed,
respectively; etching portions of the passivation layer exposed at
the predetermined electrode forming regions, thereby removing the
exposed passivation layer portions; forming the first and second
bonding electrodes at the predetermined electrode forming regions
from which the passivation layer has been removed; and removing the
photoresist film.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for manufacturing
a semiconductor light emitting device, and more particularly to a
semiconductor light emitting device manufacturing method which can
achieve an improvement in the bonding force of electrodes while
reducing the number of photoresist and lithography processes to be
carried out, by unifying processes for forming electrode and mesa
structures, thereby simplifying those processes.
[0003] 2. Description of the Related Art
[0004] In recent years, display of full range color has been
realized in accordance with development of light emitting devices
capable of emitting blue, green, and ultraviolet rays, utilizing a
gallium nitride (GaN)-based compound semiconductor.
[0005] GaN-based compound semiconductor crystals may be grown over
an insulating substrate such as a sapphire substrate. For this
reason, in the case of a GaN-based light emitting device, it is
impossible to arrange an electrode on the back surface of a
substrate. Therefore, both electrodes of the light emitting device
must be formed at the side of a semiconductor layer grown over the
substrate.
[0006] To this end, it is necessary to use a process for forming a
mesa structure in which its upper clad layer and active layer are
partially removed to partially expose the upper surface of a lower
clad layer.
[0007] Furthermore, it is necessary to provide an additional layer
so that an ohmic contact is formed by a typical electrode, because
the upper clad layer, which is made of a p type GaN layer, has a
relatively high resistance. For example, a transparent electrode
made of Ni/Au is formed prior to formation of a bonding electrode
on a p type GaN layer, thereby forming an ohmic contact for
reducing a forward voltage Vf, as disclosed in U.S. Pat. No.
5,563,422 (Assignee: Nichia Chemical Industries, Ltd.; and Date of
Patent: Oct. 8, 1996). For such a transparent electrode, an indium
titanium oxide (ITO) film may be used.
[0008] Thus, the above mentioned GaN-based semiconductor light
emitting device requires complex processes for forming a mesa
structure and an electrode structure, because of the insulating
property of its substrate for growth of GaN-based crystals. For
this reason, there is a difficulty caused by an increase in
respective numbers of photoresist processes, photoresist removal
processes, and deposition processes to be carried out for formation
of the mesa structure and electrode structure. The complexity of
such processes may be identified through exemplary processes of
FIGS. 1a to 1i.
[0009] FIGS. 1a to 1i are sectional views respectively illustrating
processes of a conventional method for manufacturing a GaN-based
semiconductor light emitting device.
[0010] In accordance with this semiconductor light emitting device
manufacturing method, a primary growth process is first carried out
to sequentially form, over a sapphire substrate 11, a first
conductivity type clad layer 13, an active layer 15, and a second
conductivity type clad layer 17, as shown in FIG. 1a. The
crystalline semiconductor layers 13, 15, and 17 may be grown in
accordance with an appropriate process such as a metal oxide
chemical vapor deposition (MOCVD) process.
[0011] Thereafter, a process for forming a mesa structure is
carried out in order to form bonding electrodes on the upper
surface of the first conductivity type clad layer 13, as shown in
FIGS. 1b and 1c. In the mesa structure forming process, a
photoresist film 21 is first formed on the second conductivity type
clad layer 15 at a region other than a region where the second
conductivity type clad layer 15 is to be etched, as shown in FIG.
1b.
[0012] Thereafter, the second conductivity type clad layer 17 and
active layer 15 are partially etched to partially expose the first
conductivity type clad layer 13, as shown in FIG. 1c. Thus, a mesa
structure is formed.
[0013] After removing the photoresist film 21 used to form the mesa
structure, a photoresist film 22 for formation of a transparent
electrode is formed on the resultant structure such that the second
conductivity type clad layer 17 is partially exposed at its upper
surface, as shown in FIG. 1d. The second conductivity type clad
layer 17 is covered by the photoresist film 22 at its edge portions
so that the edge portions are prevented from coming into contact
with an electrode to be subsequently formed adjacent to the second
conductivity type clad layer 17.
[0014] Subsequently, a transparent electrode 18 is formed at a
desired region on the second conductivity type clad layer 17 by use
of the photoresist film 22, as shown in FIG. 1e.
[0015] Thereafter, a process for forming bonding electrodes 19a and
19b on the transparent electrode 18 and the first conductivity type
clad layer 13 is carried out, as shown in FIGS. 1f to 1i. In order
to form the first bonding electrode 19a, a photoresist film 23 is
formed such that the first conductivity type clad layer 13 is
partially exposed, as shown in FIG. 1f. After formation of the
first bonding electrode 19a, the photoresist film 23 is removed, as
shown in FIG. 1g. Similarly, a photoresist film 24 is formed such
that the transparent electrode 18 is partially exposed, in order to
form the second bonding electrode 19b, as shown in FIG. 1h. After
formation of the second bonding electrode 19b, the photoresist film
24 is removed, as shown in FIG. 1i.
[0016] Thus, it is necessary to perform the photoresist process and
photoresist removal process four times for formation of the mesa
structure, transparent electrode, and first and second bonding
electrodes, respectively, in order to form a GaN-based
semiconductor light emitting device. Furthermore, each process is
complex because it involves a separate deposition process.
Additionally, a process for forming a passivation layer is involved
in the practical fabrication of semiconductor light emitting
devices. For this reason, one photoresist process and one
photoresist removal process are required, as shown in FIGS. 2a and
2b.
[0017] In accordance with a conventional process for forming a
passivation layer of a semiconductor light emitting device, a
passivation layer 20 made of SiO.sub.2 or SiN is formed over the
light emitting structure obtained after completion of the process
shown in FIG. 1i, as shown in FIG. 2a. Thereafter, a photoresist
film 25 is formed on the passivation layer 20 such that it does not
cover regions where the bonding electrodes 19a and 19b are formed,
as shown in FIG. 2b. The passivation layer 20 is then selectively
removed, using the photoresist film 25 as a mask, thereby exposing
the bonding electrodes 19a and 19b, as shown in FIG. 2c.
[0018] Thus, it is necessary to perform the photoresist process,
the photoresist removal process, and the cleaning process five
times, respectively, in order to complete a GaN-based semiconductor
light emitting device. Such an increased number of photoresist
processes to be carried out results in a complexity of the whole
process. Furthermore, there is an increased possibility of residual
foreign matters after the removal of the photoresist film. The
residual foreign matters may degrade the characteristics of the
electrode formed in the deposition process.
[0019] Moreover, the first and second bonding electrodes must be
formed in separate processes using different materials,
respectively. For this reason, the number of metal deposition
processes for formation of the electrodes is increased, so that the
whole process becomes complex.
SUMMARY OF THE INVENTION
[0020] The present invention has been made in view of the above
mentioned technical problems, and an object of the invention is to
provide a method for manufacturing a GaN-based semiconductor light
emitting device, which unifies a mesa structure forming process and
a transparent electrode forming process while implementing
electrode forming processes through a single photoresist process,
thereby being capable of simplifying the whole process while making
the manufactured semiconductor light emitting device have superior
characteristics.
[0021] In accordance with one aspect, the present invention
provides a method for manufacturing a gallium nitride-based
semiconductor light emitting device, comprising the steps of:
sequentially forming, over a substrate, a first conductivity type
clad layer, an active layer, and a second conductivity type clad
layer; forming a transparent electrode over the second conductivity
type clad layer; forming a photoresist film on the transparent
electrode such that the transparent electrode is exposed at a
predetermined region corresponding to one lateral end portion
thereof; removing respective portions of the transparent electrode,
second conductivity type clad layer, and active layer corresponding
to the predetermined region, thereby partially exposing the first
conductivity type clad layer; removing the photoresist film; and
forming first and second bonding electrodes on predetermined
portions of the transparent electrode and second conductivity type
clad layer, respectively.
[0022] Preferably, the step of partially exposing the first
conductivity type clad layer comprises the steps of wet etching the
transparent electrode at is portion corresponding to the
predetermined region, and dry etching the first conductivity type
clad layer and active layer at their portions corresponding to the
predetermined region, respectively.
[0023] The step of wet etching the transparent electrode may
comprise the step of over-etching the transparent electrode such
that the transparent electrode is undercut beneath the photoresist
film by a predetermined width. Preferably, the predetermined
undercut width of the transparent electrode corresponds to at least
3 .mu.m.
[0024] In accordance with another aspect, the present invention
provides a gallium nitride-based semiconductor light emitting
device manufacturing method in which the step of forming first and
second bonding electrodes and the step of forming a passivation
layer are carried out, using a single photoresist film. This method
comprises the steps of forming a light emitting structure including
a substrate, a first conductivity type clad layer formed over the
substrate, and an active layer, a second conductivity type clad
layer and a transparent electrode sequentially formed on the first
conductivity type clad layer at a region corresponding to one
lateral portion of the first conductivity type clad layer; forming
a passivation layer over the light emitting structure; forming a
photoresist film on the passivation layer such that the passivation
layer is exposed at predetermined regions where first and second
bonding electrodes are to be formed, respectively; etching portions
of the passivation layer exposed at the predetermined electrode
forming regions, thereby removing the exposed passivation layer
portions; forming the first and second bonding electrodes at the
predetermined electrode forming regions from which the passivation
layer has been removed; and removing the photoresist film.
[0025] Preferably, both the first and second bonding electrodes are
made of a material selected from a group consisting of Ti/Al,
Cr/Au, Cr/Ni/Au, Cr/Pt/Au, and Ti/Al/Ni/Au, so as to provide a
light emitting device having characteristics similar to those
obtained in the case in which the bonding electrodes are formed
using different materials, respectively.
[0026] In accordance with another aspect, the present invention
provides a gallium nitride-based semiconductor light emitting
device manufacturing method in which embodiments according to the
above described aspects of the present invention are combined. This
method comprises the steps of: sequentially forming, over a
substrate, a first conductivity type clad layer, an active layer,
and a second conductivity type clad layer; forming a transparent
electrode over the second conductivity type clad layer; forming a
photoresist film on the transparent electrode such that the
transparent electrode is exposed at a predetermined region
corresponding to one lateral end portion thereof; etching
respective portions of the transparent electrode, second
conductivity type clad layer, and active layer corresponding to the
predetermined region, thereby partially exposing the first
conductivity type clad layer; forming a passivation layer over a
light emitting structure obtained after completion of the etching
step adapted to partially expose the first conductivity type clad
layer; forming a photoresist film on the passivation layer such
that the passivation layer is exposed at predetermined regions
where first and second bonding electrodes are to be formed,
respectively; etching portions of the passivation layer exposed at
the predetermined electrode forming regions, thereby removing the
exposed passivation layer portions; forming the first and second
bonding electrodes at the predetermined electrode forming regions
from which the passivation layer has been removed; and removing the
photoresist film.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The above objects, and other features and advantages of the
present invention will become more apparent after reading the
following detailed description when taken in conjunction with the
drawings, in which:
[0028] FIGS. 1a to 1i are sectional views respectively illustrating
processes of a conventional semiconductor light emitting device
manufacturing method;
[0029] FIGS. 2a to 2c are sectional views respectively illustrating
a passivation process included in the conventional semiconductor
light emitting device manufacturing method; and
[0030] FIGS. 3a to 3f are sectional views respectively illustrating
processes of a method for manufacturing a GaN-based semiconductor
light emitting device.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] Now, preferred embodiments of the present invention will be
described in detail with reference to the annexed drawings.
[0032] FIGS. 3a to 3f are sectional views respectively illustrating
processes of a method for manufacturing a GaN-based semiconductor
light emitting device.
[0033] In accordance with this semiconductor light emitting device
manufacturing method, a primary growth process is first carried out
to sequentially form, over a substrate for growth of GaN crystals,
that is, a sapphire substrate 31, a first conductivity type clad
layer 33, an active layer 35, and a second conductivity type clad
layer 37, as shown in FIG. 3a.
[0034] The crystalline semiconductor layers 33, 35, and 37 may be
grown in accordance with an appropriate process such as an MOCVD
process. Prior to the growth of the first conductivity type clad
layer 33, a buffer layer (not shown) made of, for example, AlN/GaN,
may be formed in order to improve the lattice alignment of the
first conductivity type clad layer 33 with the sapphire substrate
31. The first conductivity type clad layer 33 may be comprised of
an n type GaN layer and an n type AlGaN layer, whereas the second
conductivity type clad layer 37 may be comprised of a p type GaN
layer and a p type AlGaN layer. The active layer 35 may be
comprised of an undoped InGaN layer having a multi-quantum well
structure.
[0035] Thereafter, a transparent electrode layer 38 is formed over
the second conductivity type clad layer 37, as shown in FIG. 3b. A
photoresist film 41 is then formed on the transparent electrode
layer 38 such that the transparent electrode layer 38 is exposed at
a region corresponding to its one lateral end portion. The
transparent electrode layer 38 may be made of an Ni/Au alloy.
Preferably, the transparent electrode layer 38 may be comprised of
an ITO layer. The exposed region not covered by the photoresist
film 41 defines a region where an etching process for forming a
mesa structure is to be subsequently carried out in order to
partially expose the first conductivity type clad layer 33.
[0036] Subsequently, the second conductivity type clad layer 37 and
active layer 35 are partially removed in accordance with an etching
process at their portions corresponding to the region exposed
region not covered by the photoresist film 41, thereby partially
exposing the first conductivity type clad layer 33, as shown in
FIG. 3c. Thus, the resultant light emitting structure has a mesa
structure. In the etching process for removing desired portions of
the second conductivity type clad layer 37 and active layer 35, the
first conductivity type clad layer 33 may also be partially
removed, as shown in FIG. 3c.
[0037] The mesa structure forming process involves two etching
processes, that is, a primary etching process for removing a
portion of the transparent electrode 38 corresponding to the
exposed region, and a secondary etching process for removing
portions of the second conductivity type clad layer 37 and active
layer 35 corresponding to the exposed region. The primary etching
process is carried out in accordance with a wet etching method,
whereas the secondary etching process is carried out in accordance
with a dry etching method.
[0038] As apparent from the above description, in accordance with
the present invention, the mesa structure forming process and the
transparent electrode forming process are carried out by use of one
photoresist film, that is, the photoresist film 41, so that there
is an improvement over the conventional case in which the mesa
structure forming process and the transparent electrode forming
process are carried out by use of two photoresist films, that is,
the photoresist films 21 and 22 of FIG. 1. In accordance with such
a unified photoresist film forming process, it is possible to
reduce respective numbers of photoresist removal processes and
cleaning processes inevitably involved in photoresist film forming
processes. In particular, where the transparent electrode is
comprised of an ITO film, there is an additional advantage in that
the transparent electrode is subjected to sufficient oxidation
required for an improvement in transmissivity as it is sufficiently
exposed in subsequent processes, because it is formed at a stage
earlier than that in the conventional case, that is, at a stage
prior to the etching process for formation of the mesa
structure.
[0039] In the conventional case, different photoresist films are
used for the transparent electrode forming process and the mesa
structure forming process, respectively, in order to form the
transparent electrode such that each edge thereof is spaced apart
from an adjacent edge of the second conductivity type clad layer by
a certain distance. Generally, the second conductivity type clad
layer exhibits a weakness against discharge of static electricity
at its sharp edges. Accordingly, it is necessary to form the
transparent electrode such that each edge thereof is spaced apart
from an adjacent edge of the second conductivity type clad layer,
so as to suppress injection of current through the sharp edges. To
this end, upon forming the transparent electrode, the conventional
case utilizes a separate photoresist film other than the
photoresist film used for the formation of the mesa structure.
[0040] In accordance with the present invention, however, it is
possible to form the transparent electrode 38 such that each edge
thereof is spaced apart from an adjacent edge of the second
conductivity type clad layer 37 by a predetermined distance d,
while using a single photoresist film, that is, the photoresist
film 41, for both the patterning of the transparent electrode 38
and the formation of the mesa structure. This can be achieved by
performing the wet etching process for partially removing the
transparent electrode 38, in an over-etching manner, such that the
transparent electrode 38 arranged beneath the photoresist film 41
is undercut by a predetermined width d. Preferably, the
predetermined width d is at least 3 .mu.m in order to prevent
discharge of static electricity.
[0041] Thereafter, processes for forming a passivation layer and
bonding electrodes in accordance with the present invention are
carried out. These processes are illustrated in FIGS. 3d to 3f.
[0042] A passivation layer 40 is first formed over the entire upper
surface of the light emitting structure, obtained after completion
of the process shown in FIG. 3c and removal of the photoresist film
41, including respective exposed surfaces of the transparent
electrode 38, and first and second conductivity type clad layers 33
and 37, as shown in FIG. 3d. As is well known, the passivation
layer 40 may be made of an appropriate material such as SiO.sub.2
or SiN.
[0043] A photoresist film 422 is then formed on the passivation
layer 40 such that the passivation layer 40 is exposed at regions
where bonding electrodes are to be formed, respectively, as shown
in FIG. 3e. The boding electrode forming regions correspond to
regions where desired portions of the transparent electrode 38 and
first conductivity type clad layer 33 are positioned. These regions
are arranged so that they are spaced apart from each other by a
sufficient distance while being symmetrically arranged.
[0044] Thereafter, the exposed portions of the passivation layer 40
are etched, using the photoresist film 42 as a mask, so that they
are removed, thereby exposing corresponding portions of the
transparent electrode 38 and first conductivity type clad layer 33.
Subsequently, a bonding electrode 39a for a p type conductivity and
a bonding electrode 39b for an n type conductivity are formed on
the exposed portions of the transparent electrode 38 and first
conductivity type clad layer 33, respectively, as shown in FIG. 3f.
Thus, a GaN-based semiconductor light emitting device is
completed.
[0045] As described above, the processes for forming the
passivation layer and bonding electrodes are carried out, using
only one photoresist film, that is, the photoresist film 42, in
accordance with the present invention. Therefore, it is preferable
to use the same metallic material for both the electrodes 39a and
39b in the bonding electrode forming process, so as to
simultaneously form the electrodes 39a and 39b. For the electrode
forming material, Ti/Al, Cr/Au, Cr/Ni/Au, Cr/Pt/Au or Ti/Al/Ni/Au
may be used.
[0046] In accordance with the present invention, the photoresist
film 42 for formation of the bonding electrodes is formed under the
condition in which the passivation layer 40 has been formed. Also,
the bonding electrodes are formed at regions from which the
passivation layer 40 is removed, using the photoresist film 42 as a
mask. Accordingly, there is no or little photoresist at the
electrode forming regions after removal of the passivation layer
40, even when the photoresist film 42 is incompletely removed.
Therefore, it is possible to solve a problem of a degraded bonding
force of the bonding electrodes caused by residual photoresist. It
is also possible to dispense with cleaning processes. The above
mentioned problem may also occur in the transparent electrode
forming process, as described above in conjunction with FIGS. 1d
and 1e. In accordance with the present invention, however, the
problem caused by residual photoresist can be solved because a
desired photoresist film is formed after formation of the
transparent electrode, as described in conjunction with FIGS. 3b
and 3c. Also, it is possible to improve the bonding force of the
transparent electrode.
[0047] The improvement in the bonding forces of the transparent
electrode and bonding forces achieved along with a process
simplification in accordance with the present invention may also
contribute to an improvement in the reliability of the finally
obtained device. Where the bonding electrodes were practically made
of the same metal, for example, a Ti/Au alloy, without using
different metals suitable to respective associated clad layers, in
accordance with the present invention, the resultant light emitting
device exhibited characteristics (a forward voltage of 3.25V and an
optical efficiency of 12.2 mcd at 20 mA) substantially similar to
those of conventional light emitting devices (a forward voltage of
3.29V and an optical efficiency of 12.4 mcd).
[0048] Although the embodiment illustrated in FIGS. 3a to 3f has
been described as a combination of the embodiment (FIGS. 3a to 3c)
in which the transparent electrode forming process and the mesa
structure forming process are unified, and the embodiment (FIGS. 3d
to 3f) in which the passivation layer forming process and the
bonding electrode forming process are unified, it may be
implemented under the condition in which the embodiments of FIGS.
3a to 3c and FIGS. 3d to 3f are separately implemented. For
example, the embodiment of FIGS. 3a to 3c may be implemented in a
state of being combined with conventional processes of forming a
passivation layer and bonding electrodes. Also, the embodiment of
FIGS. 3d to 3f may be implemented in a state of being combined with
conventional processes of forming a mesa structure and a
transparent electrode.
[0049] Although the preferred embodiments of the invention have
been disclosed for illustrative purposes, those skilled in the art
will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
[0050] As apparent from the above description, the present
invention provides a method for manufacturing a GaN-based
semiconductor light emitting device, which is capable of
implementing processes for forming a mesa structure and a
transparent electrode by use of a single photoresist film, thereby
simplifying those processes, implementing processes for forming a
passivation layer and electrodes by use of a single photoresist
film, thereby simplifying the whole process, easily forming a
transparent electrode pattern suitable to prevention of
electrostatic discharge (ESD), in accordance with an over-etching
process, and preventing a degradation in the bonding forces of the
transparent electrode and bonding electrodes caused by residual
photoresist.
* * * * *